1. Field of the Invention
This invention relates to the field of fluid flow devices and nozzles and, especially to nozzles producing a laminar output stream of water. Still more particularly, this invention relates to nozzles capable of producing a laminar trajectory stream suitable for water displays and fountains.
2. Prior Art
Various methods and theories have been used in the past for producing a laminar stream of water or other fluid by reducing the turbulence in a supply stream prior to discharge from a nozzle, spout, or faucet.
Laminar flow is characterized by the smooth and regular flow of fluid in layers. It has, therefore, been naturally assumed that the creation of laminar flow may best be accomplished by forcing the flow stream into a number of small flow paths substantially axial to the flow of the fluid through the body of the device. In this way, the Reynolds number for the flow in each path can be reduced to a value in the laminar region. The Reynolds number is a dimensionless value which indicates whether flow in a particular application can be expected to be laminar or turbulent. The relationship between the Reynolds numbers and the velocity of the stream, the diameter of the flow area, and the kinematic viscosity of the fluid is stated by the following equation: EQU Nr=vD/V
where:
Nr=Reynolds Number
v=velocity of the stream
D=diameter of the flow area
V=kinematic viscosity of the fluid
For practical applications, a Reynolds number less than 2,000 generally indicates laminar flow and a value over 4,000 predicts turbulent flow. The range between 2,000 and 4,000 is called the critical region and the type of flow cannot be predicted due to the possible influence of outside factors such as pipe roughness. In fact, by minimizing these external disturbances, it is possible to maintain laminar flow for Reynolds number values as high as 50,000.
Since the kinematic viscosity is fixed for water, the only way to reduce the Reynolds number is to minimize the flow path diameter or the velocity. Reducing the diameter of the flow area have most often been accomplished through the use of perforated discs, multiple layers of screens, channels, fins, tubes, etc., placed in the flow path to promote straight and parallel flow in small segments over the flow area of the stream with the net result being the discharge of a larger laminar stream.
Such prior art methods do reduce the amount of turbulence in short streams as required for splashless and silent flow of water in lavatories, drinking fountains, and tubs. However, they are not, in general, suitable for use in fountain displays in which the flow stream must often remain clear, laminar, and coherent, over a trajectory path more than 10 feet high and 15 feet distant. Layered screens act to divide and redirect the flow in a uniform vertical direction but leave room for radial and rotational flow in the spaces between layers which may pass intact through the relatively thin screens or perforated discs, causing turbulence in the stream and requiring a nozzle body of relatively long length.
Other methods used, such as tubes or channels, remove rotational and radial flow, also by dividing and redirecting flow in the axial direction through small flow areas. Fuller, U.S. Pat. No. 4,795,092, discloses a laminar flow fountain nozzle in which a porous foam member having small flow paths therethrough but providing "a very high restriction and very large viscous surfaces to any flow in the tangential direction" is used in conjunction with a flow straightening stack of small tubular members. Such nozzles, however, must rely on a relatively large nozzle body diameter to reduce the velocity components in the axial direction.
Another source of turbulence reduced by the present invention is often introduced at the discharge outlet or orifice. As flow exits the nozzle body through the relatively small flow area of the output stream, it must accelerate. The stream will continue to neck down after exiting the nozzle to a cross-section smaller than that of the nominal stream diameter. This area of minimum cross section is called the "vena contracta." Beyond this point, the stream must decelerate again and expand. This contraction and expansion causes turbulence in the stream and an energy loss. This energy loss and the associated turbulence are dependent upon the geometry of the nozzle discharge outlet. The energy loss is calculated from the equation: EQU H1=Cl(v/2G)
where: where:
H1=energy loss
v=velocity of the stream
G=acceleration due to gravity
C1=a loss coefficient suggested from experimental data relating to exit geometry
For a given velocity, the energy loss is shown to be directly related to the value of the loss coefficient. It is known that the loss coefficient for a sharp-edged orifice is approximately, C1=0.5, while for a chamfered outlet, C1=0.25, and for a smooth, gradual contraction, C1=0.05. While these values of the loss coefficient are approximate, they do not provide a general indication the magnitude of difference in energy loss and turbulence introduced by the exit geometries used in prior art.
The primary object of the present invention is to provide a nozzle which produces a laminar output stream suitable for water displays and fountains. A further object is to provide a laminar flow nozzle which minimizes flow disturbances within the nozzle to such a degree as to allow laminar flow at higher Reynolds number values than would normally be associated with laminar flow. Still another object is to provide a smaller, and thus more versatile, laminar flow nozzle suitable for water displays and fountains than is possible in the prior art and which is also less expensive to manufacture.